During the proposed grant period, investigation of the development of rabbit hippocampus will be continued. Studies will be carried out in the in vitro slice preparation. Using electrophysiological, pharmacological, and anatomical techniques, we shall evaluate the plasticity of hippocampal connections following deafferenting lesions in animals of various ages. Cell membrane characteristics and synaptic potentials will be compared to those seen in normal animals of comparable ages. Sensitivities to putative transmitter substances, and changes in morphological organization will also be studied. A comparison will be made between changes seen when lesions are made in immature vs mature animals. These experiments will show what compensatory mechanisms are used in a specific region of the central nervous system in response to injury.